A Noble Metal assisted Color Tuning of Upconversion Nanoparticles for Multi-Level Security application

Abstract

We developed luminescence color transition of rare-earth-doped upconverting nanocrystals (UCNs) by incorporating noble metal nanoparticles into UCNs embedded microparticles. UCNs have attracted interest due to their unique optical property emitting visible light by absorbing continuous-wave near infrared light (NIR). The luminescence color of UCNs is decided by relative ratio of the lanthanide dopants and it has always been challenging to realize an emission color tuning after UCN synthesis. Here, we synthesized noble metal nanoparticles in the polymeric 3D structure. Surface plasmon resonance (SPR) band of metal nanoparticle permits the UCNs color transition by absorbing specific emission peaks of UCNs. Metal nanoparticles with different morphologies have various SPR band which allow both of optical color transition under the visible light and luminescent color transition under the NIR light. This dual-color transition system opens a new horizon for multi-level security application.